1. Field of the Invention
The present invention relates to venting of equipment used in water, an amphibious waterproof equipment used on land and in water of up to several meters depth or waterproof equipment normally used on land, and more particularly to a vent valve provided between a battery housing arranged in the equipment and an outer wall of the equipment.
2. Related Background Art
An example of the vent valve is disclosed in Japanese Laid-Open Utility Model Application No. 56-115863 in which a vent valve is provided in a peripheral wall on battery housing of a land equipment rather than underwater equipment.
Where a vent valve is to be provided between a battery housing arranged in underwater equipment and an outer wall of the equipment, it is necessary to take into account a possibility of leak of water into the battery housing from a location external of the equipment through the vent valve. Since there is no known useful way, it has not been put into practice.
Where a battery is to be housed in the battery housing in the equipment, the following attention is to be paid. If the battery 1 is left for a long time while it is housed, electrolyte leaks from the battery and may ruin a battery circuit. In order to prevent this, the battery housing may be isolated to keep it in air tight, but if the battery generates heat, and the electrolyte therein is vaporized, gas of a high pressure is externally discharged by the vaporization. In the air tight state of the battery housing, a pressure in the housing rises by the discharged gas of the battery and the housing may break.
In order to avoid such a risk, a vent valve is required as disclosed in the above-mentioned Japanese Laid-Open Utility Model Application No. 56-115863. The pressure in the battery housing rises by the discharged gas of the battery and the vent valve is actuated by the pressure to allow the gas to be externally discharged through the vent valve. However, the vent valve disclosed in the above application is complex in structure and high in cost. Further, when the pressure in the battery housing abnormally rises and a large volume of gas is discharged all at once, it is a question whether the gas may be instantly discharged and there is a risk of break of the battery housing.
In an underwater equipment, when the vent valve is actuated and gas is externally discharged, that is, into water, water may penetrate into the battery housing through the vent valve which is open during venting, depending on the attitude of the equipment. As a result, parts such as the battery may be eroded or the electric circuit may be ruined.